Liquid crystal display

ABSTRACT

The liquid crystal display device having an array substrate ( 10 ) provided with a pixel electrode ( 3 ) disposed in a region defined by two adjacent gate wirings ( 1 ) and two adjacent source wirings ( 2 ), a switching element ( 5 ) for switching a voltage applied to the pixel electrode ( 3 ) from the source wiring ( 2 ) based on a signal volume fed from the gate wiring ( 1 ), a common wiring ( 8 ) formed between the two adjacent gate wirings ( 1 ), a common electrode ( 4 ) being electrically connected to the common wiring ( 8 ) and generating an electric field between the common electrode ( 4 ) and the pixel electrode ( 3 ) for driving the liquid crystal, and a storage capacity electrode ( 20   a ) electrically connected to the common wiring ( 8 ), wherein the common wiring ( 8 ) and the storage capacity electrode ( 20   a ) are layered so as to hold at least some part of the pixel electrode ( 3 ) in between through insulating layers ( 6   a,    6   b ).

TECHNICAL FIELD

[0001] The present invention relates to a liquid crystal display device,specifically a liquid crystal display device of an IPS (In-PlaneSwitching) style.

BACKGROUND ART

[0002] Active matrix type liquid crystal displays employing thin-filmtransistors (TFTs) are used in various fields as displays for TV sets,camcorders, personal computers, personal word processors and the likebecause they can be made thin and light and driven with a low voltage.There is a large market for such displays.

[0003] In recent years, particularly for use in TV sets and computers,the demand for liquid crystal display devices having a wide viewingangle, usable for wide screens, has increased. In order to meet thisdemand, Japanese Unexamined Patent Publication No. 1994-160878 proposes,as a method for increasing the viewing angle of liquid crystal displaydevices, an IPS (In-Plane Switching) method in which the pixel electrodeand the opposing electrode for driving the liquid crystal are formed ona single substrate where liquid crystal molecules are actuated byapplying a voltage in a lateral direction. This display method is alsoknown as the lateral electric field method or comb-like electrodemethod, where the liquid crystal molecules are arranged so that themajor axes thereof are parallel with respect to the substrate, andtherefore the liquid crystal molecules are never oriented perpendicularto the substrate. Thus, the variance in brightness when seen fromvarious directions becomes less and this makes it possible to achieve awide viewing angle.

[0004] A known IPS style liquid crystal display device will be describedbelow with reference to drawings.

[0005]FIG. 11 is a plan view illustrating the structure of one pixel ofan array substrate of a prior art liquid crystal display device. FIGS.12(a) and (b) respectively show cross sections taken along lines P-P′and Q-Q′ of FIG. 11. In FIG. 11, gate wirings 1 for feeding scanningsignals and source wirings 2 for feeding image signals are disposed soas to intersect at approximately right angles. Nearby each intersectionof a gate wiring 1 and a source wiring 2, a thin-film transistor (TFT) 5having semiconductor layers is formed as a switching element. To thesource wiring 2, a comb-like pixel electrode 3 is connected via the TFT5, and a common electrode 4 functioning as a standard potential isarranged so as to mesh with the pixel electrode 3. The common electrode4 is electrically coupled to a common wiring 8 disposed between the twogate wirings 1 and 1 in a parallel manner.

[0006] As shown in FIGS. 11 and 12, the gate wiring 1, the commonelectrode 4 and the common wiring 8 are formed on an array substrate 10as a same layer. Upon this layer, the source wiring 2 and the pixelelectrode 3 are formed as a same layer through an insulating layer 6 a.At the intersection of the common wiring 8 and the pixel electrode 3,with the insulating layer 6 a in between, a storage capacity region 109is formed. The principal components of the wirings and the electrodesmentioned above include aluminum (Al), chromium (Cr), tantalum (Ta),molybdenum (Mo) and like metals.

[0007] On the surface of an opposing substrate 14 facing the arraysubstrate 10, a black matrix 12 and a color filter 13 are formed. Asshown by dash-dot-dot lines in FIG. 11, the black matrix 12 is arrangedso as to cover the TFT 5 and the non-controlled area of the electricfield generated between the gate wiring 1 or the source wiring 2 and thepixel electrode 3 or the common electrode 4. The color filter 13 isformed on the aperture of the black matrix 12, and each pixel thereofhas a color layer of red, green or blue so that, in the liquid crystaldisplay device as a whole, these three colors are repeated in an array.

[0008] Between the array substrate 10 and the opposing substrate 14,liquid crystal (not shown) is sealed in the gap held constant by beadsapplied on the substrate. Thus a liquid crystal display device can beobtained.

[0009] According to such a liquid crystal display device, the variancebetween the voltage applied to the pixel electrode 3 and that of thecommon electrode 4, to which standard potential is applied, generates anelectric field substantially parallel to the substrate, and the electricfield is applied to the liquid crystal disposed between the electrodes.By storing electric charge while the TFT 5 is in an on-status, even whenthe leakage of electric charge from the pixel electrode 3 occurs, thestorage capacity region 109 can supply the voltage for the leakedportion and maintain the signal voltage at a certain level. This enablesthe liquid crystal to remain actuated.

[0010] The pixel electrode 3, the common electrode 4 and the commonwiring 8 of the above-described liquid crystal display device are madeof opaque metals, preventing light from passing through these areas. Ifthe area where the pixel electrode 3 and the common wiring 8 formingstorage capacity region 109 intersect is too small, the storage capacitybecomes insufficiently small, resulting in flicker and crosstalk.Therefore, the storage capacity region 109 must have at least a certainminimal size; however, making the storage capacity region 109 largerleads to a wider non-light-transmitting area. Even in the area wherelight is transmitted, in some locations such as the gap between thesource wiring and the gate wiring, and the common electrode and thepixel electrode, etc., it is not possible to control the lighttransmittance as much as is desired. Therefore, these locations shouldbe covered with the black matrix 12.

[0011] Consequently, the known IPS style liquid crystal display devicehas drawbacks such as a low pixel aperture, i.e., unsatisfactory ratioof the effective display area to the area of pixel, leading to a panelwith low luminance.

DISCLOSURE OF THE INVENTION

[0012] An object of the invention is to provide a liquid crystal displaydevice for use in an IPS style liquid crystal panel which displaysbright, high quality images by enhancing the aperture ratio whilemaintaining the capacity of the storage capacity region of the pixels.

[0013] In order to achieve the above objects, the liquid crystal displaydevice of the invention comprises an array substrate, an opposingsubstrate facing the array substrate, and liquid crystal held betweenthe array substrate and the opposing substrate. The array substrate isprovided with a plurality of gate wirings and a plurality of sourcewirings intersecting each other, a pixel electrode disposed in a regiondefined by two adjacent gate wirings and two adjacent source wirings, aswitching element for switching a voltage applied to the pixel electrodefrom the source wiring based on a signal volume fed from the gatewiring, a common wiring formed between the two adjacent gate wirings, acommon electrode being electrically connected to the common wiring andgenerating an electric field between the common electrode and the pixelelectrode creating a voltage for driving the liquid crystal, and astorage capacity electrode electrically connected to the common wiring.The common wiring and the storage capacity electrode are layered so asto hold at least some part of the pixel electrode in between through aninsulating layer.

[0014] In this liquid crystal display device, at the intersection ofcommon wiring, the storage capacity electrode and the pixel electrode,when seen from a planar view, the storage capacity region is formed.This allows the liquid crystal display device to store electric chargenot only between the common wiring and the pixel electrode but alsobetween the pixel electrode and the storage capacity electrode, andtherefore the capacity per unit area thereof increases compared to thatof known ones. Accordingly, even when the area of the storage capacityis made smaller, high quality of the displayed image can be maintained.This makes it possible to enhance the aperture ratio.

[0015] The liquid crystal display device can further comprise anadditional storage capacity electrode electrically connected to thepixel electrode. In this case, the pixel electrode and the additionalstorage capacity electrode are layered so as to hold at least some partof the common wiring or the storage capacity electrode in betweenthrough the insulating layer. In this arrangement, it is also possibleto store electric charge between the common wiring or the storagecapacity electrode and the additional storage capacity electrode.Thereby, the capacity per unit area thereof further increases, enhancingthe aperture ratio.

[0016] In this liquid crystal display device, it is possible to layerthe common wiring, the pixel electrode and the storage capacityelectrode in this order, form a light shading film made of the samematerial as the storage capacity electrode on the same layer as thestorage capacity electrode, and cover the switching element with thelight shading film. This arrangement reliably prevents backlight andoutside light from directly striking a switching element, such as a TFT,etc., and thereby current leakage from the switching element can beprevented. This reduces crosstalk and flicker, etc., improving the imagequality. It is possible to form the light shading film and the storagecapacity electrode at the same time, and therefore an additional processis not needed.

[0017] Furthermore, in this liquid crystal display device, it ispossible to form the common wiring and the gate wiring on a same layerand the storage capacity electrode and the common electrode on a samelayer. According to this arrangement, the gate wiring is formed on aseparate layer from that of the storage capacity electrode and thecommon electrode through an insulating layer. Therefore, there is norisk of the gate wiring causing short-circuit between the commonelectrode or the pixel electrode, and the ends of the common electrodeand the pixel electrode can be extended to the gate wiring. This canwiden the region where the drive of liquid crystal is controllable andfurther improve the aperture ratio.

[0018] To achieve the above objects, the liquid crystal display deviceof the invention comprises an array substrate, an opposing substratefacing the array substrate, and liquid crystal held between the arraysubstrate and the opposing substrate, wherein the array substrate isprovided with a plurality of gate wirings and a plurality of sourcewirings intersecting each other, a pixel electrode disposed in a regiondefined by two adjacent gate wirings and two adjacent source wirings, aswitching element for switching a voltage applied to the pixel electrodefrom the source wiring based on a signal volume fed from the gatewiring, a common wiring formed between the two adjacent gate wirings, acommon electrode being electrically connected to the common wiring andgenerating an electric field between the common electrode and the pixelelectrode creating a voltage for driving the liquid crystal, and astorage capacity electrode electrically connected to the common wiring,the pixel electrode and the storage capacity electrode are layered so asto hold at least some part of the common wiring in between through theinsulating layer.

[0019] According to this liquid crystal display device, the storagecapacity region is formed at the intersection of the pixel electrode,the storage capacity electrode and the common wiring, when seen from aplanar view, and electric charge can be stored not only between thecommon wiring and the pixel electrode but also between the common wiringand the storage capacity electrode, increasing the capacity per unitarea of the storage capacity region than that of known ones. Therefore,it is possible to maintain a high level of image quality even when thearea of the storage capacity region is made smaller, and this makes itpossible to enhance the aperture ratio.

[0020] The liquid crystal display device can further comprise anadditional storage capacity electrode electrically connected to thecommon wiring. In this case, the common wiring and the additionalstorage capacity electrode are layered so as to hold at least some partof the pixel electrode or the storage capacity electrode in betweenthrough the insulating layer. In this arrangement, electric charge canalso be stored between the pixel electrode or the storage capacityelectrode and the additional storage capacity electrode. This furtherincreases the capacity per unit area of the storage capacity region, andenhances the aperture ratio.

[0021] To achieve the above objects, a liquid crystal display devicecomprises an array substrate, an opposing substrate facing the arraysubstrate and liquid crystal held between the array substrate and theopposing substrate, wherein the array substrate is provided with aplurality of gate wirings and a plurality of source wirings intersectingeach other, a pixel electrode disposed in a region defined by twoadjacent gate wirings and two adjacent source wirings, a switchingelement for switching a voltage applied to the pixel electrode from thesource wiring based on a signal volume fed from the gate wiring, acommon wiring formed between the two adjacent gate wirings, and a commonelectrode being electrically connected to the common wiring andgenerating an electric field between the common electrode and the pixelelectrode creating a voltage for driving the liquid crystal, whereinboth the pixel electrode and the common electrode are formed on aseparate layer from that of the gate wiring and the ends of the pixelelectrode and the common electrode overlap with the gate wiring. Forexample, in this liquid crystal display device, it is possible to formthe gate wiring from a first conductive layer and form the pixelelectrode and the common electrode from a second conductive layer.

[0022] This arrangement is free from light leakage from the gap betweenthe pixel electrode or the common electrode and the gate wiring, as theends of the pixel electrode and the common electrode overlap with thegate wiring. Therefore, formation of a black matrix becomes unnecessaryon the area corresponding to this overlap in the opposing layer,enhancing the aperture ratio. It is preferable that the length of thearea where the pixel electrode and the common electrode overlap with thegate wiring be 1 to 5 μm along the longitudinal direction of the pixelelectrode or the common electrode.

[0023] It is also preferable that the common electrode be formed on aseparate layer from that of the source wiring through the insulatinglayer, and at least some part thereof overlap with the source wiring inthe longitudinal direction. This prevents light leakage from the gapbetween the source wiring and the common electrode, and therefore thearea of the opposing substrate where formation of a black matrix isneeded becomes smaller, enhancing the aperture ratio.

[0024] Alternatively, the pixel electrode and the common electrode canbe formed on different layers through the insulating layer for reliablypreventing short-circuit between the two. For example, it is possible toform the gate wiring from a conductive layer, form the pixel electrodefrom a second conductive layer, form the common electrode from a thirdconductive layer, and insulate each interlayer between the first tothird conductive layers by a first and a second insulating layer.

[0025] It is also preferable that the gate wiring, the pixel electrodeand the common electrode be layered in this order, and a light shadingfilm made of the same material as the common electrode be formed on thesame layer as the common electrode for covering the switching element.This allows simultaneous formation of the light shading film and thecommon electrode, improving image quality without adding anymanufacturing steps. The aperture ratio can further be enhanced becauseformation of a black matrix is not needed in the area corresponding tothe switching element on the opposing substrate. Alternatively, it canbe so structured that no black matrix formation is conducted on theopposing substrate, simplifying the manufacturing process. It ispreferable that the switching element be formed on the gate wiring inorder to prevent light leakage from around the switching element.

[0026] When the gate wiring, the pixel electrode and the commonelectrode are layered in this order, it is preferable that an insulatinglayer formed between the pixel electrode and the common electrode have athickness of 0.5 μm or greater and it is also preferable that theinsulating layer be made of an organic film. This satisfactorily reducesthe parasitic capacity generated in the area where the gate wiring andthe common electrode overlap one another and further improves imagequality.

[0027] In each of the liquid crystal display devices described above,the pixel electrode and/or the common electrode can be made oftransparent electrode materials, and thereby the aperture ratio can beenhanced. It is also possible to form the storage capacity electrode sothat from one end, where the signal from the gate wiring is fed in, tothe other end the electrode becomes smaller. This prevents flicker.BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a firstembodiment of the invention, and

[0029]FIG. 1(b) is a cross-sectional view taken along line A-A′ of FIG.1(a).

[0030]FIG. 2(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a secondembodiment of the invention, and

[0031]FIG. 2(b) is a cross-sectional view taken along line B-B′ of FIG.2(a).

[0032]FIG. 3(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a thirdembodiment of the invention, and

[0033]FIG. 3(b) is a cross-sectional view taken along line C-C′ of FIG.3(a).

[0034]FIG. 4(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a fourthembodiment of the invention, and

[0035]FIG. 4(b) is a cross-sectional view taken along line D-D′ of FIG.4(a).

[0036]FIG. 5 shows test results in connection with the fourth embodimentof the invention.

[0037]FIG. 6 is a cross-sectional view of a modified form of the fourthembodiment of the invention.

[0038]FIG. 7(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a fifthembodiment of the invention, and

[0039]FIG. 7(b) is a cross-sectional view taken along line E-E′ of FIG.7(a).

[0040]FIG. 8(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a sixthembodiment of the invention, and FIG. 6(b) is a cross-sectional viewtaken along line F-F′ of FIG. 8(a).

[0041]FIG. 9(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a seventhembodiment of the invention, and

[0042]FIG. 9(b) is a cross-sectional view taken along line G-G′ of FIG.9(a).

[0043]FIG. 10(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to an eighthembodiment of the invention, and

[0044]FIG. 10(b) is a cross-sectional view taken along line H-H′ of FIG.10(a).

[0045]FIG. 11 is a plan view illustrating the structure of one pixel ofan array substrate of a prior art liquid crystal display device.

[0046]FIG. 12(a) is a cross-sectional view taken along line P-P′ of FIG.11, and

[0047]FIG. 12(b) is a cross-sectional view taken along line Q-Q′ of FIG.11.

BEST MODE FOR CARRYING OUT THE INVENTION

[0048] Embodiments of the present invention will be described below withreference to the accompanying drawings. It is to be noted that, in thefollowing descriptions, those elements which are identical to theelements of the known liquid crystal display described above areidentified with the same reference symbols, and repetitious explanationwill be omitted.

[0049] First Embodiment

[0050]FIG. 1(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a firstembodiment of the invention, and FIG. 1(b) is a cross-sectional viewtaken along line A-A′ of FIG. 1(a).

[0051] Similar to the prior art liquid crystal display device describedabove, in the liquid crystal display device according to the presentembodiment, a storage capacity region 9 a is formed in the area where acommon wiring 8 and a pixel electrode 3 intersect each other through aninsulating layer 6 a. The liquid crystal display device of the presentembodiment is different from known ones in that a storage capacityelectrode 20 a is formed upon the pixel electrode 3 in the storagecapacity region 9 a.

[0052] In other words, an insulating layer 6 b is formed on top of asource wiring 2 and the pixel electrode 3, which are formed as a samelayer on top of the insulating layer 6 a. On top of the insulating layer6 b, the storage capacity electrode 20 a is formed so as to beelectrically connected to the common wiring 8 via contact holes 30 a and30 b created in the insulating layers 6 a and 6 b. The storage capacityregion 9 a is formed in a manner such that the storage capacityelectrode 20 a and the common wiring 8 hold some part of the pixelelectrode 3 in between through the insulating layers 6 a and 6 b.

[0053] The liquid crystal display device according to the presentembodiment can be manufactured by the following steps. On a glass platewhich will serve as an array substrate 10, a first conductive layerhaving a principal component such as aluminum (Al) is deposited byspattering or the like. Then, the plate is patterned into a complanateform by photolithography, thus obtaining the gate wiring 1, the commonelectrode 4 and the common wiring 8.

[0054] A first insulating layer 6 a made of silicon nitride (SiNx), etc.is deposited by the CVD method or the like. After forming asemiconductor layer made of a-Si, etc. by the CVD method,photolithography or the like, a second conductive layer is subjected topatterning in the same manner as the first conductive layer, obtainingthe source wiring 2, the pixel electrode 3 and a TFT 5 serving as aswitching element. The widths of the pixel electrode 3 and the commonelectrode 4 are, for example, 3 to 8 μm and the gap between the two is,for example, 10 to 15 μm.

[0055] After forming a second insulating layer 6 b in the same manner asthe first insulating layer 6 a, the contact holes 30 a and 30 b areformed in the first insulating layer 6 a and the second insulating layer6 b by photolithography.

[0056] Thereafter, the storage capacity electrode 20 a is obtained byforming a third conductive layer followed by patterning in the samemanner as the first conductive layer, and then is electrically connectedto the common wiring 8 via the contact holes 30 a and 30 b. On the topsurface of the thus obtained array substrate, a fourth insulating layercan be formed for protecting the TFT and the electrode.

[0057] There is no limitation to the materials to be used for theforegoing first to third conductive layers; however, preferable aremetal materials having a low wiring resistance such as aluminum (Al) andlike metals, etc. Furthermore, each conductive layer can be a monolayerfilm or a multiplayer film.

[0058] On the other hand, on a glass substrate serving as an opposingsubstrate 14, film formation is conducted by spattering or the likeusing chromium (Cr) metal and pattern formation is achieved byphotolithography for obtaining a conductive black matrix 12. Then,resins each having one of the RGB elements (the three colors) arepatterned into the area forming the pixels in order, thus obtainingcolor filters 13 arranged in a dot pattern. In order to preventcontamination of the liquid crystal layer caused by Cr etc., an overcoatlayer can be formed over the entire surface of color opposing substrateby using acrylic or like resins. It is also possible to form the blackmatrix using a resin material. In this case, film formation can beconducted by applying resin by spin coating, printing or a like method,and therefore the manufacturing costs can be reduced.

[0059] After applying oriented films (not shown) to the facing surfacesof the thus obtained substrates 10 and 14, rubbing is conducted in aprescribed direction. Thereafter, the substrates are bonded together onthe edges by a sealer with a resin spacer held in between. Then, liquidcrystal (not shown) is sealed therein, obtaining a liquid crystaldisplay device.

[0060] In the peripheral part of the liquid crystal display device, agate driving circuit is connected to the end of the gate wiring 1 and asource signal driving circuit is connected to the end of the sourcewiring 2. Thereby, each of the driving circuits makes the liquid crystaldisplay device operate in accordance with the signals input from acontroller. Operation of the liquid crystal display device will beexplained below.

[0061] Firstly, scanning signals and image signals fed from the externalcircuits are input into the individual gate wirings 1 and the individualsource wirings 2, respectively. By the scanning signals fed through thegate wiring 1, the TFT 5 connected to the gate wiring 1 is selectivelyturned on or off. Thereby, the image signals fed therein via the sourcewiring 2 while the TFT 5 is in an on-status are fed to the pixelelectrode 3. An electric field is generated by the potential differencebetween the pixel electrode 3 and the common electrode 4, and therebyperformance of the liquid crystal oriented between the electrodes iscontrolled. On the array substrate side of the liquid crystal panel, abacklighting (not shown) comprising a cold-cathode tube is disposed, andthe assignment of intensity levels is achieved by controlling the driveof the liquid crystal.

[0062] When the TFT 5 is in an off-status, feed of picture-signalvoltage into the pixel electrode 3 is stopped; however, the liquidcrystal is kept in operation using the electric charge stored in thestorage capacity region 9 a. The storage capacity region 9 a of thepresent embodiment can store electric charge by generating potentialdifferences between the common wiring 8 and the pixel electrode 3 andbetween the pixel electrode 3 and the storage capacity electrode 20 a,and therefore the capacity per unit area becomes larger than that of thestorage capacity region 109 of the known liquid crystal display devicedescribed above. This allows the area of overlap of the electrodes to becut approximately in half. As a result, the aperture ratio of the pixelis enhanced and a high display luminance can be obtained.

[0063] (Second Embodiment)

[0064]FIG. 2(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a secondembodiment of the invention, and FIG. 2(b) is a cross-sectional viewtaken along line B-B′ of FIG. 2(a).

[0065] The liquid crystal display device of the second embodiment hasthe same structure as that of the first embodiment in that a storagecapacity region is composed of a common wiring, a pixel electrode and astorage capacity electrode, and differs from the first embodiment inthat the storage capacity electrode is electrically connected to thepixel electrode.

[0066] Precisely, a storage capacity electrode 20 b is formed on anarray substrate 10 and a gate wiring 1, a common electrode 4 and acommon wiring 8 are formed thereon via an insulating layer 6 a. On topthereof, a source wiring 2, a pixel electrode 3 and a TFT 5 are formedhaving an insulating layer 6 b thereunder. In some part of the commonwiring 8, an aperture 81 is formed. The storage capacity electrode 20 band the pixel electrode 3 are electrically connected via a contact hole30 c formed in the insulating layers 6 a and 6 b so as to pass throughthe substantial center of the aperture 81. A storage capacity region 9 bis formed in a manner such that the storage capacity electrode 20 b andthe pixel electrode 3 hold a part of the common wiring 8 in betweenthrough the insulating layers 6 a and 6 b.

[0067] By using the storage capacity region 9 b of the presentembodiment, electric charge can be stored by generating potentialdifferences both between the storage capacity electrode 20 b and thecommon wiring 8 and between the common wiring 8 and the pixel electrode3. Therefore, the capacity per unit area thereof is larger than that ofthe storage capacity region 109 of the prior art liquid crystal displaydevice described above. This allows the area of overlap of theelectrodes to be cut approximately in half. As a result, the apertureratio of the pixel is enhanced and a high display luminance can beobtained.

[0068] (Third Embodiment)

[0069]FIG. 3(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a thirdembodiment of the invention, and FIG. 3(b) is a cross-sectional viewtaken along line C-C′ of FIG. 3(a).

[0070] The liquid crystal display device of the third embodiment is thesame as the liquid crystal display device of the first embodiment in allrespects except that it further comprises an additional storage capacityelectrode.

[0071] Precisely, an insulating layer 6 c is formed on a storagecapacity electrode 20 a and, on the insulating layer 6 c, an additionalstorage capacity electrode 20 d is formed. The additional storagecapacity electrode 20 d is electrically connected to a pixel electrode 3through a contact hole 30 d located on the insulating layers 6 b and 6c. Thereby, a storage capacity region 9 c is formed at the intersectionof common wiring 8, the pixel electrode 3, the storage capacityelectrode 20 a and the additional storage capacity electrode 20 d, whenseen from a planar view.

[0072] In the storage capacity region 9 c of the present embodiment,potential differences are individually generated between the commonwiring 8 and the pixel electrode 3, between the pixel electrode 3 andthe storage capacity electrode 20 a and between the storage capacityelectrode 20 a and the additional storage capacity electrode 20 d,allowing storage of electric charge. Therefore, the capacity per unitarea thereof further increases compared to the storage capacity regionsof the first and second embodiments. As a result, the aperture ratio ofthe pixel is enhanced and a high display luminance can be obtained.

[0073] In the liquid crystal display device of the present embodiment,on top of the additional storage capacity electrode 20 d, anotherstorage capacity electrode can be deposited. In other words, by layeringelectrodes so as to overlap each other with holding an insulating layerin between in a manner such that a first storage capacity electrode iselectrically connected to the common wiring 8 and a second storagecapacity electrode is electrically connected to the pixel electrode 3,the capacity per unit area of the storage capacity region is furtherenhanced.

[0074] The liquid crystal display device of the second embodiment canalso be provided with an additional storage capacity electrode on thepixel electrode thereof through the insulating layer. By electricallyconnecting the additional storage capacity electrode to the commonwiring 8 via a contact hole, an effect similar to that of presentembodiment can be achieved.

[0075] (Fourth Embodiment)

[0076]FIG. 4(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a fourthembodiment of the invention, and FIG. 4(b) is a cross-sectional viewtaken along line D-D′ of FIG. 4(a).

[0077] The liquid crystal display device according to the fourthembodiment comprises a light shading film 15 a made of the same materialas the storage capacity electrode 20 a which is formed on the same layeras a storage capacity electrode 20 a. In other respects, theconstruction thereof is the same as that of the first embodiment.

[0078] This arrangement allows simultaneous formation of the lightshading film 15 a and the storage capacity electrode 20 a, and thereforeadditional steps for obtaining the light shading film 15 a areunnecessary. By covering the top of the TFT 5 with the light shadingfilm 15 a, deterioration of image quality attributable to backlight oroutside light, which is inherent in the TFTs, can be prevented.

[0079]FIG. 5 is a graph showing the relationship between the gate-drainvoltage and the source-drain current both with and without the lightshading film. As shown in the figure, when the light shading film 15 ais not provided, even when the gate-drain voltage is 0 or lower, i.e.,when the TFT is in an off-status, current flows between the source andthe drain. As a result, the pixel potential fluctuates, leading todrawbacks such as deterioration of image quality caused by crosstalk,etc.

[0080] Alternatively, when the light shading film 15 a is provided, whenthe gate-drain voltage is 0 or lower, i.e., when the TFT is in anoff-status, little current flows between the source and the drain.Therefore, the above drawbacks can be eliminated, improving the imagequality.

[0081] As shown in FIG. 6, it is possible to form the light shading film15 a and the storage capacity electrode 20 a at the same time on a flatsurface of a flattened film 22 a made of silicon nitride (SiNx) or thelike formed on the insulating layer 6 b of the first embodiment by theCVD method, etc. When the flattened film 22 a is formed as describedabove, the parasite capacitance inherently generated between the lightshading film 15 a and the TFT 5 can be reduced. This makes it possibleto reduce the load on the TFT 5 and stabilize the operation on the TFT5. Furthermore, the turbulence of the orientation of the sealed-inliquid crystal is minimized, obtaining a further improved display imagequality.

[0082] (Fifth Embodiment)

[0083]FIG. 7(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display according to a fifthembodiment of the invention, and FIG. 7(b) is a cross-sectional viewtaken along line E-E′ of FIG. 7(a).

[0084] In the liquid crystal display device according to the firstembodiment, the common electrode is formed on the same layer as thecommon wiring. The fifth embodiment is different from the firstembodiment in that, the common electrode is formed on the same layer asa storage capacity electrode. In other respects, the construction of thefifth embodiment is the same as that of the first embodiment.

[0085] Precisely, a gate wiring 1 and a common wiring 8 are formed on anarray substrate as a same layer. Upon the layer, a source wiring 2 and apixel electrode 3 are formed as a same layer through an insulating layer6 a. On top thereof, a storage capacity electrode 20 a and a commonelectrode 4 are formed through an insulating layer 6 b. The commonelectrode 4 is electrically connected to the common wiring 8 via contactholes 30 a and 30 b formed in the storage capacity electrode 20 a andthe insulating layers.

[0086] As similar to the first embodiment, this structure allows theoverlap area of the electrodes to become approximately half of the knownstorage capacity region 9, leading to an enhanced aperture ratio ofpixel. Furthermore, the pixel electrode 3 and the common electrode 4 areformed on a separate layer from that of the gate wiring 1 with havingthe insulating layers 6 a and 6 b in between. This arrangement makes itpossible to extend the ends of the pixel electrode 3 and the commonelectrode 4 to the gate wiring 1 without the risk of the pixel electrode3 or the common electrode 4 causing a short-circuit with the gate wiring1, and make the region where the drive of the liquid crystal iscontrollable wider in each pixel. Accordingly, this also enhances theaperture ratio.

[0087] When the ends of the pixel electrode 3 and the common electrode 4overlap with the gate wiring 1, as indicated by the widths shown by thedash-dot-dot lines of FIG. 7(a), it is not necessary to form a blackmatrix along the gate wiring 1. In this case, it is preferable that thelength where the ends of the pixel electrode 3 and the common electrode4 overlap with the gate wiring 1 be 1 μm or greater with taking thealignment error into consideration. However, when the overlapping areabecomes unduly large, parasitic capacitance becomes too large and thismay cause rounding of signals of the gate wiring 1, and therefore it ispreferable that the length be 5 μm or less.

[0088] (Sixth Embodiment)

[0089]FIG. 8(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display device according to asixth embodiment of the invention, and FIG. 6(b) is a cross-sectionalview taken along line F-F′ of FIG. 8(a).

[0090] In the liquid crystal display device of the fifth embodiment, thestorage capacity electrode 20 a and the common electrode 4 are formed onthe insulating layer 6 b; in the liquid crystal display device of thesixth embodiment, a storage capacity electrode 20 a and a commonelectrode 4 are formed on an insulating layer 6 b on a flattened film 22b. In other respects, the construction of the sixth embodiment is thesame as that of the fifth embodiment.

[0091] According to this construction, the common electrode 4 canreadily be arranged so as to overlap with a part of a source wiring 2along the longitudinal direction thereof. Thereby, there is no leakageof light from a gap between the source wiring 2 and the electrode 4.Therefore, the region where drive of the liquid crystal is controllableis made further wider and the aperture ratio can be enhanced. In thiscase, it is not necessary to form a black matrix on an opposingsubstrate 14 on the area corresponding to this overlap.

[0092] As same as in the fourth embodiment, in the present embodiment, alight shading film can be formed on the same layer as the storagecapacity electrode 20 a and the common electrode 4 in the area as showby a dash-dot-dot line in FIG. 8(a). Employing this construction makesit possible not only to obtain a liquid crystal display deviceexhibiting a high level of image quality but also to simplify themanufacturing steps thereof by obviating the need to form a black matrixon the opposing substrate 14. As shown in FIG. 8(a), it is preferablethat TFT 5 be formed on the gate wiring 1 for preventing leakage oflight from around the TFT 5.

[0093] The flattened film 22 b can be made of a silicon oxide film, asilicon nitride film or the like. However, it is preferable that thefilm be made of an organic film such as photosensitive acrylic resin formaking the parasitic capacity generated in the area where the gatewiring 1 and the common electrode 4 overlap each other satisfactorilysmall. It is more preferable that the film thickness be 0.5 μm orgreater. This diminishes problems such as crosstalk, etc. and furtherimproves the display image quality. It is appropriate that the averagethickness of the flattened film 22 b be about 3 μm.

[0094] (Seventh Embodiment)

[0095]FIG. 9(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display device according to aseventh embodiment of the invention, and FIG. 9(b) is a cross-sectionalview taken along line G-G′ of FIG. 9(a).

[0096] The liquid crystal display device of the seventh embodimentdiffers from the prior art liquid crystal display device shown in FIGS.11 and 12 in that, in the prior art device, the common electrode 4 isformed on the same layer as the common wiring 8; however, in the liquidcrystal display device of the seventh embodiment, a common electrode 4is formed on a separate layer from that of the common wiring 8 and thesame as that of a pixel electrode 3. In other respects, the constructionof the liquid crystal display device of the present embodiment is thesame as that of the known one.

[0097] Precisely, a gate wiring 1 and the common wiring 8 are formed onan array substrate 10 as a same layer. Upon thereof, through aninsulating layer 6 a, a source wiring 2, a pixel electrode 3 and thecommon electrode 4 are formed as a same layer. The common electrode 4 iselectrically connected to the common wiring 8 formed in the insulatinglayer 6 a via a contact hole 30 e. A storage capacity region 9 d isformed in the area where the pixel electrode 3 and the common wiring 8overlap each other through the insulating layer 6 a.

[0098] Similar to the fifth embodiment, this arrangement allows the endsof the pixel electrode 3 and the common electrode 4 to overlap with thegate wiring 1 and widens the region where drive of liquid crystal iscontrollable. On an opposing substrate 14, formation of a black matrixbecomes unnecessary on the area corresponding to this overlap, enhancingthe aperture ratio. As the same reason described in the fifthembodiment, it is preferable that the length of the area where the endsof the pixel electrode 3 and the electrode 4 overlap with the gatewiring 1 be from 1 μm to 5μm.

[0099] (Eighth Embodiment)

[0100]FIG. 10(a) is a plan view illustrating a structure of one pixel ofan array substrate of a liquid crystal display device according to aneighth embodiment of the invention, and FIG. 10(b) is a cross-sectionalview taken along line H-H′ of FIG. 10(a).

[0101] The liquid crystal display device of the seventh embodiment andthe eighth embodiment are different in that, in the seventh embodiment,the pixel electrode 3 and the common electrode 4 are formed on the samelayer as the source wiring 2, and, in the eighth embodiment, a pixelelectrode 3 and a common electrode 4 are formed on a separate layer froma source wiring 2 through a flattened film 22 c. In other respects, theconstruction of the eighth embodiment is the same as that of the seventhembodiment.

[0102] Precisely, a source wiring 2 is formed on a gate wiring 1 and thecommon wiring 8 formed on an array substrate 10 through an insulatinglayer 6 a. Upon thereof, the pixel electrode 3 and the common electrode4 are formed as a same layer through the flattened film 22 c. The drainend of a TFT 5 is connected to the pixel electrode 3 via a contact hole30 f.

[0103] According to this arrangement, it is possible to overlap at leastsome part of the common electrode 4 with the source wiring 2 along thelongitudinal direction thereof, and therefore there is no risk of lightleakage from a gap between the source wiring 2 and the common electrode4. Accordingly, formation of a black matrix on an opposing substrate 14becomes unnecessary on the area corresponding to this overlap, furtherenhancing the aperture ratio.

[0104] Similar to the fourth embodiment, as shown in a dash-dot-dot linein FIG. 10(a), a light shading film 15 c can be formed on the same layeras the pixel electrode 3 and the common electrode 4. Employing thisarrangement makes it possible not only to obtain a liquid crystaldisplay device exhibiting a high level of image quality but also toreduce the manufacturing processes because formation of the black matrixon the opposing substrate 14 becomes unnecessary.

[0105] The pixel electrode 3 and the common electrode 4 can be formed asseparate layers having an insulating layer in between. This reliablyprevents short-circuit between the pixel electrode 3 and the commonelectrode 4.

[0106] (Other Embodiments)

[0107] Above, each embodiment of the invention is explained in detail.The precise embodiments of the invention, however, are not limited tothese embodiments. For example, in the embodiments described above, thecommon electrode and the pixel electrode are metal electrodes; however,they can be formed as transparent electrodes made of ITO(Indium-Tin-Oxide), etc. This arrangement can further enhance theaperture ratio.

[0108] In each embodiment described above, when seen from a planar view,it is preferable that the storage capacity region is shaped so as tobecome smaller from one end, where the signal from the gate wiring isfed in, to the other end. This allows keeping a voltage applied to theliquid crystal to be substantially constant in each pixel withoutchanging the main wiring and the shape of the electrode. Accordingly,generation of flicker can be prevented while eliminating drawbacks suchas the breaking of wires, etc. Thus, the display image quality can beimproved.

[0109] Furthermore, each pixel region defined by a plurality of gatewirings and a plurality of source wirings arranged in a matrix is notlimited to a rectangular shape and may be a rhomboid-like shape.

1. A liquid crystal display device comprising: an array substrate; anopposing substrate facing the array substrate; and liquid crystal heldbetween the array substrate and the opposing substrate, wherein thearray substrate is provided with: a plurality of gate wirings and aplurality of source wirings intersecting each other; a pixel electrodedisposed in a region defined by two adjacent gate wirings and twoadjacent source wirings; a switching element for switching a voltageapplied to the pixel electrode from the source wiring based on a signalvolume fed from the gate wiring; a common wiring formed between the twoadjacent gate wirings; a common electrode being electrically connectedto the common wiring and generating an electric field between the commonelectrode and the pixel electrode creating a voltage for driving theliquid crystal; and a storage capacity electrode electrically connectedto the common wiring, wherein the common wiring and the storage capacityelectrode are layered so as to hold at least some part of the pixelelectrode in between through an insulating layer.
 2. The liquid crystaldisplay device according to claim 1 further comprising: an additionalstorage capacity electrode electrically connected to the pixelelectrode, wherein the pixel electrode and the additional storagecapacity electrode are layered so as to hold at least some part of thecommon wiring or the storage capacity electrode in between through theinsulating layer.
 3. The liquid crystal display device according toclaim 1, wherein the common wiring, the pixel electrode and the storagecapacity electrode are layered in this order; a light shading film madeof the same material as the storage capacity electrode is formed on thesame layer as the storage capacity electrode; and the switching elementis covered with the light shading film.
 4. The liquid crystal displaydevice according to claim 1, wherein the common wiring is formed on thesame layer as the gate wiring and the storage capacity electrode isformed on the same layer as the common electrode.
 5. A liquid crystaldisplay device comprising: an array substrate; an opposing substratefacing the array substrate; and liquid crystal held between the arraysubstrate and the opposing substrate, wherein the array substrate isprovided with: a plurality of gate wirings and a plurality of sourcewirings intersecting each other; a pixel electrode disposed in a regiondefined by two adjacent gate wirings and two adjacent source wirings; aswitching element for switching a voltage applied to the pixel electrodefrom the source wiring based on a signal volume fed from the gatewiring; a common wiring formed between the two adjacent gate wirings; acommon electrode being electrically connected to the common wiring andgenerating an electric field between the common electrode and the pixelelectrode creating a voltage for driving the liquid crystal; and astorage capacity electrode electrically connected to the common wiring,wherein the pixel electrode and the storage capacity electrode arelayered so as to hold at least some part of the common wiring in betweenthrough an insulating layer.
 6. The liquid crystal display deviceaccording to claim 5 further comprising: an additional storage capacityelectrode electrically connected to the common wiring, wherein thecommon wiring and the additional storage capacity electrode are layeredso as to hold at least some part of the pixel electrode or the storagecapacity electrode in between through the insulating layer.
 7. A liquidcrystal display device comprising: an array substrate; an opposingsubstrate facing the array substrate; and liquid crystal held betweenthe array substrate and the opposing substrate, wherein the arraysubstrate is provided with: a plurality of gate wirings and a pluralityof source wirings intersecting each other; a pixel electrode disposed ina region defined by two adjacent gate wirings and two adjacent sourcewirings; a switching element for switching a voltage applied to thepixel electrode from the source wiring based on a signal volume fed fromthe gate wiring; a common wiring formed between the two adjacent gatewirings; and a common electrode being electrically connected to thecommon wiring and generating an electric field between the commonelectrode and the pixel electrode creating a voltage for driving theliquid crystal, wherein both the pixel electrode and the commonelectrode are formed on a separate layer from that of the gate wiringand the ends of the pixel electrode and the common electrode overlapwith the gate wiring.
 8. The liquid crystal display device according toclaim 7, wherein the common electrode is formed on a separate layer fromthat of the source wiring through an insulating layer, and at least somepart thereof is overlapped with the source wiring along the longitudinaldirection thereof.
 9. The liquid crystal display device according toclaim 7, wherein the pixel electrode and the common electrode are formedon separated layers through an insulating layer.
 10. The liquid crystaldisplay device according to claim 9, wherein the gate wiring, the pixelelectrode and the common electrode are layered in this order, a lightshading film made of the same material as the common electrode is formedon the same layer as the common electrode, and the switching element iscovered with the light shading film.
 11. The liquid crystal displaydevice according to claim 10, wherein at least some part of theswitching element is formed on the gate wiring.
 12. The liquid crystaldisplay device according to claim 9, wherein the gate wiring, the pixelelectrode and the common electrode are layered in this order, and theinsulating layer formed between the pixel electrode and the commonelectrode is made of an organic film having a thickness of 0.5 μm orgreater.
 13. The liquid crystal display device according to any one ofclaims 1, 5 or 7, wherein the pixel electrode and/or the commonelectrode are made of a transparent electrode material.
 14. The liquidcrystal display device according to claims 1 or 5, wherein the storagecapacity electrode is shaped so as to become smaller from one end, wherethe signal from the gate wiring is fed in, to the other end.